Add detection for various aarch64 CPU features already supported by LLVM and Linux.
This commit adds feature detection for the following features:
- FEAT_CSSC
- FEAT_ECV
- FEAT_FAMINMAX
- FEAT_FLAGM2
- FEAT_FP8
- FEAT_FP8DOT2
- FEAT_FP8DOT4
- FEAT_FP8FMA
- FEAT_HBC
- FEAT_LSE128
- FEAT_LUT
- FEAT_MOPS
- FEAT_LRCPC3
- FEAT_SVE_B16B16
- FEAT_SVE2p1
- FEAT_WFxT
It also adds feature detection for FEAT_FPMR. It is somewhat of a
special case because FPMR only exists as a feature in LLVM 18, it has
been removed from the LLVM upstream. On that account the intention is
for it to be detectable at runtime through stdarch but not have a
corresponding compile-time Rust target feature.
Linux features: https://github.com/torvalds/linux/blob/master/arch/arm64/include/uapi/asm/hwcap.h
LLVM features: llvm-project/llvm/lib/Target/AArch64/AArch64.td
